Rolling diaphragm device with inertia force compensating means



March 12, 1968 J. A. RIETDIJK 3,372,624

ROLLING DIAPHRAGM DEVICE WITH INERTIA FORCE COMPENSATING MEANS Filed Nov. 30, 1965 I5 Sheets-Sheet l i PRIORART INVENTOR. JOHAN A.. RIETDIJK March 12, 1968 J. A. RIETDIJK 3,372,624

ROLLING DIAPHRAGM DEVICE WITH INERTIA FORCE COMPENSATING MEANS Filed Nov. 30, 1965 3 Sheets-Sheet 2 INVENTOR. mm: A. RIETDIJK gm. 4 z.

AGENT J- A. RIETDIJK March 12, 1968 ROLLING DIAPHRAGM DEVICE WITH INERTIA FORCE COMPENSATING MEANS Filed Nov. 50, 1965 3 Sheets-Sheet 3 TTPKWY FiGS INVENTOR- JOHAN A. RIETDIJK AGEN United States Patent Ofiice Patented Mar. 12, 1968 3,372,624 ROLLING DIAPHRAGM DEVICE WITH INERTIA FORCE COMPENSATING MEANS Johan Adriaan Rietdijk, Emmasingel, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Nov. 30, 1965, Ser. No. 510,499 Claims priority, application Netherlands, Dec. 10, 1964, G t-14,339 7 Claims. (Cl. 92--84) ABSTRACT OF THE DISCLGSURE A cylinder with two out-of-phase pistons reciprocating therein having a rolling diaphragm seal between one piston and the cylinder and an inertia force compensating means connected to both pistons and being either a mass and a pivoting lever, or a cable-pulley system.

The invention relates to a device comprising at least one cylinder and a first piston-like body adapted to move therein for varying the volume of a working space, the seal between said first piston-like body and the cylinder wall being formed by one or more rolling diaphragms, each of which engages by one side a liquid, said device comprising means for maintaining on each of the rolling diaphragms a pressure difference which is substantially constant at least during each stroke, the first piston-like body being, by its side remote from the working space, in contact with a liquid which is in contact with a second piston-like body, coupled with a driving gear.

In devices of the kind according to the invention it is essential that the rolling diaphragm in operation should always be stretched and the stress in the rolling diaphragm should not become excessively great, since otherwise break-down may occur. It has furthermore been found that it is particularly conducive for the lifetime of the rolling diaphragm to maintain a substantially constant value of the pressure difference on the rolling diaphragm.

In a known device of the kind set forth the aforesaid conditions for optimum operation of the rolling diaphragm are obtained by supporting the rolling diaphragm on one side from a liquid. The supporting liquid is accommodated in a space which is bounded not only by the rolling diaphragm but also by rigid Wall portions of the relatively movable elements, which wall portions are for-med so that the space maintains a constant volume during the movement only by its shape. Such a quantity of liquid is provided in said space that a pressure diiference prevails constantly on the rolling diaphragm.

This known structure has the disadvantage that if for some reason or other the quantity of liquid in the space below the rolling diaphragm varies or if the volume of this space does not remain constant due to inaccuracy of the dimensions of the rigid wall portions, the pressure difference on the rolling diaphragm and hence the stress therein will vary. In order to withstand the varying difference in pressure the rolling diaphragm will vary its length, which adversely affects the lifetime thereof.

In order to obviate said disadvantage it has been proposed to arrange the rolling diaphragm with its side facing the second piston-like body on the said liquid provided between the two piston-like bodies, the first pistonlike body being engaged by resilient members for maintaining a pressure difference on said body. If in this known device a greater or smaller quantity of liquid is present in the space between the two piston-like bodies than the quantity corresponding to the desired pressure difference on the rolling diaphragm, due to excessively slow response of a control-member or due to leakage of liquid, the rolling diaphragm will not vary its length but the distance between the two piston-like bodies will change. In this way the correct pressure difference is maintained on the rolling diaphragm substantially without variation of the length of the rolling diaphragm, even if the conditions vary quite rapidly. The second piston-like body and the cylinder may have a step-wise structure at the area of the co-operative wall portions, so that during the movement of the piston-like bodies the volume of the space between the two piston-like bodies need not vary.

It has been found that in this known device the inertia forces of the first piston-like body will play a part, since they produce fluctuations of the pressure difference pre vailing on the rolling diaphragm and the first piston-like body. The rolling diaphragm is affected by said pressure fluctuations so that its length will vary and the lifetime is thereby adversely affected.

In order to mitigate said limitation, the device according to the invention is characterized in that the side of the rolling diaphragm facing the second piston-like body also engages said liquid provided between the two pistonlike bodies and in that resilient members apply to the first piston-like body for maintaining a pressure dilference on said body, said device comprising means for compensating the inertia forces of the first piston-like body and, as the case may be, the inertia forces of a quantity of liquid having substantially a volume equal to that of the space bounded by the side of the first piston-like body engaging the liquid and the tangential plane of the rolling diaphragm at right angles to the center line of the device in the central position of the piston-like bodies, to an extent such that these forces do not substantially affect the pressure difference on the rolling diaphragm and the first pistonlike body.

In a further advantageous embodiment of the device according to the invention the means for compensating the inertia forces of the first piston-like body, and as the case may be, the inertia forces of said quantity of liquid are formed by one or more compensation masses connected with the first and the second piston-like bodies so as to be freely movable, this connection being such that the inertia forces of said masses apply to the first pistonlike body and are opposite the inertia forces of the first piston-like body and of the liquid.

A further advantageous embodiment of the device according to the invention is characterized in that each of the compensation masses co-operates with a lever, which is pivoted to the first and the second piston-like bodies, the pivotal connection with the second piston'rlike body being located between the place where each compensation mass applies to the relevant lever and the junction of said lever with the first piston-like body. In this way an extremely simple structure is obtained for completely compensating the inertia forces of the first piston-like body and of said liquid.

According to a further advantageous aspect the resilient members maintaining a pressure difference on the rolling diaphragm apply to the compensation masses. With a suitable choice of the transmission ratio, the resilient members may be of a considerably lighter structure than in the case in which they apply directly to the first pistonlike body. It is furthermore possible in this case to avoid a fixed connection between the compensation mass and the lever and to provide resilient members which urge said mass against the lever. In one direction the inertia forces are then exerted directly on the lever, whereas in the other direction the inertia forces produce a variation in the contact pressure between the lever and the mass, so that the influences of the ineltia forces are compensated in both directions.

A further embodiment of the device according to the invention is characterized in that each of the compensation masses is linked through a cable-pulley system to the first and the second piston-like bodies so that the inertia forces of the first piston-like body and, as the case may be, those of the liquid are compensated by the inertia forces of the compensation masses. In this case again the resilient members provide a prestress of the cable, so that the inertia forces are compensated in both directions.

In a further embodiment of the device according to the invention each of the compensation masses and the relevant lever and the relevant cable-pulley system are located in the liquid between the two piston-like bodies, so that an extremely compact structure is obtained.

Since the inertia forces of the compensation masses are transferred through a lever or a cable-pulley system to the first piston-like body, it is possible to choose the transmission ratio so that the compensation mass may be considerably smaller than the mass of the first piston-like body.

From the foregoing it will be apparent that the invention provides an extremely simple construction for reducing the detrimental effect of the inertia forces of the first piston-like body and those of the liquid at any number of revolutions.

The invention will be described more fully with reference to the drawing, which shows diagrammatically, not to scale, a few embodiments of piston-cylinder combinations.

FIG. 1 shows diagrammatically a known combination of a cylinder and a piston adapted to move therein.

FIGS. 2, 3 and 4 show diagrammatically in sectional views four different combinations of a piston and a cylinder, comprising a compensation mass co-operating with a lever for compensating the inertia forces of the hydraulically driven piston.

FIGS. 5 and 6 show diagrammatically in sectional view a piston-cylinder combination in which the hydraulically driven piston is linked through a cable and a number of pulleys to the compensation mass.

eferring to FIG. 1, reference numeral 1 designates a cylinder, in which a piston 2 is adapted to move. The piston 2 bounds by one side a working space 3, which may be the compression space of a compressor or the compressionor expansion-space of a thermodynamic reciprocating engine. The other side of the piston 2 engages a liquid column 4, which in turn engages a piston 5, which is linked through a connecting rod 6 to a crank 7, which can be driven in known manner (not shown). The seal between the piston 2 and the cylinder 1 is formed by a rolling diaphragm 8. The space 4 communicates with a control-member which provides a constant pressure difference on the rolling diaphragm 8 and ensures a given flow of liquid through the space 4, in order to avoid an excessive concentration of medium due to difusion through the rolling diaphragm.

This control-member is formed by a liquid pump 9, which can supply liquid through a duct 10 to the space 4. The wall of the piston 5 is provided with a hole 11 (if desired a plurality of holes), which co-operates with part of the inner wall of the piston 2. When the position of the piston 2 relative to that of the piston 5 deviates from the positions of said pistons corresponding to a desired pressure difference the piston 2 will leave the hole 11 free or block it. When the hole 11 is free, liquid can flow from the space 4 back into the casing, so that the distance between the pistons 5 and 2 is reduced. When the hole 11 is blocked, the pump 9 pushes liquid into the space 4, so that the distance between the pistons 2 and 5 will increase. In normal operation the lower side of the piston 2 will intersect the hole 11, so that liquid can constantly flow out of the space 4 and the liquid is thus continuously replenished by the pump 9.

The piston 2 is engaged by one or more pressure springs 19, which ensure that the pressure in the liquid in the space 4 is always a given amount lower than the pressure in the workin space 3. These springs have a fairly flat characteristic curve so that in the event of a variation of the distance between the pistons the pressure difference is scarcely varied.

If for some reason or other a greater quantity of liquid is drained from the space 4 than the quantity supplied through the duct 10, the consequences for the rolling diaphragm S are not serious. The pressure springs 19 will only become slightly shorter while the distance between the pistons 2 and 5 is slightly reduced. If in another instant a greater quantity of liquid is supplied, the distance between the pistons will regain its initial value. All this does not adversely affect the rolling membrane.

This known device has the disadvantage that at a high number of revolutions and/or a small diameter of the piston the inertia forces of the piston 2 give rise to troublesome fluctuations of the pressure difference on the rolling diaphragm.

The inertia forces giving rise to fluctuations of the pressure difference are equal to M w r sin wt, wherein M is the mass of the piston 2 plus the mass of a quantity of the liquid having a volume corresponding to the space bounded by the inner side of the piston 2 and the plane A-A tangential to the rolling diaphragm in the central position of the pistons 2 and 5.

w is the angular velocity of the crank with which the piston 5 is connected through the connecting rod 6-.

r is the radius of the crank.

The inertia forces produce an additional pressure difference on the rolling diaphragm and on the piston 2 equal to:

sin wt in which d and d designate the diameters of the pistons 2 and 5 respectively.

The fluctuations of the pressure due to the inertia forces bring about unwanted variations in length of the rolling diaphragm 8, which may thus have a shorter lifetime.

Additional pressure fluctuations due to the inertia forces of the piston 2 may be completely obviated at any number of revolutions by means of the structure shown in the piston 2. In this structure the pistons 2 and 5 are interconnected by a level 30. At the places 31 and 32 the lever 30 is pivoted to the pistons 2 and 5 respectively. The lever 30 is furthermore provided with a weight 33, which is connected through a draw spring 34 with the piston 5.

Upon the movement of the pistons 2 and 5 the weight 33 will move with the same speed. The inertia forces of the weight .33 are operative in the same direction as those of the piston 2, but they are transferred through the lever 30 to the piston 2 so that they are opposite those of the piston 5. When the distances 2: and a between the weight 33 and the pivotal point 32 and between the pivotal points 32 and 31 and the masses M and m of the weight 33 and of the piston 2 plus the quantity of liquid are in a given relationship, the inertia forces of the piston 2 and of the quantity of liquid are just compensated by the inertia forces of the weight 33. This situation applies when m=a/bM. By a suitable choice of a/ b (smaller than 1, which will usually be the case in practice), the force of the spring 34 may be considerably smaller than that of the springs 19 in the structure of FIG. 1.

A different embodiment of a piston-cylinder combination is shown in FIG. 3. The sole difference from the structure of FIG. 2 consists in that the convex side of the rolling diaphragm faces the working space. This means that in this structure the liquid pressure must always slightly exceed the pressure in the working space 3. Therefore, in this structure thespring 34 is formed by a pressure spring.

In the embodiment shown in FIG. 4 the weight 33 is not rigidly secured to the lever 30, but it engages the same with pre-stress at point 36. The upwardly orientated inertia forces of the weight 33 are directly transferred to the lever36 and through the latter to the piston 2 so that in this direction on the inertia forces of the piston 2 and of part of the liquid are again compensated. The inertia forces of the weight 33 in the other direction produce a compression of the draw spring 34, which means that the tensile force is reduced, so that the pressure difference on piston 2 is lower. On the other hand the inertia forces of the piston 2 minus those of part of the liquid just produce an increase in liquid pressure. These two effects just compensate each other, so that the influence of the inertia forces on the pressure difference is again neutralized.

FIGS. 2 to 4 show, for the sake of clarity, only one compensation weight 33 with the associated lever. It will be obvious that for reasons of symmetry for example two weights may be used. These two weights are then located one on each side ofthe axis of symmetry and are arranged on parallel levers.

FIG. 5 shows the construction of a piston-cylinder combination in which the compensation weight 33 is not arranged on a lever, but is connected through a cab1e-pulley system with the pistons 2 and 5. At the place 38 a cable 39 is linked to the lower side of the weight 33 and passes from point 38 to a pulley 40 seated on a shaft 41 rigidly secured to the piston 5. From the pulley 40 the cable 39 passes to a pulley 42, which is secured to a shaft 43 fixed to the piston 2. Then the cable passes along the pulleys 43, 44, 45, 46 and 48 and is then again secured at the place 49 to the lower side of the weight 33. It will be apparent that the set of pulleys may be extended at will or diminished. The mass m of the weight 33 and the mass M of the piston 2 plus the mass of the liquid located above the level of the upper point of the diaphragm in such a pulley system are at a ratio equal to the transmission ratio of said system. This means that in the structure shown in FIG. 5 m= /sM. The weight 33 is furthermore subjected to a pressure spring 50, which provides a given amount of preliminary stress for the cable 39, so that the pressure in the liquid is always higher than the pressure in the working space 3 by a given amount. This means that the convex side of the rolling diaphragm 8 faces the working space. In the event of inertia forces in upward direction the stress of the cable 39 will increase due to the inertia forces of the weight 33, so that the inertia forces of the piston 2 are just compensated. If, on the contrary, inertia forces occur in downward direction, the prestress of the cable 39 will be reduced by the inertia forces of the weight 33. Thus the influence of the inertia forces of the piston 2 on the pressure difference of said piston is just neutralized.

Finally FIG. 6 shows a piston-cylinder combination in which the inertia forces are compensated by a compensation weight 33, which is linked to the pistons 2 and 5 through a cable-pulley system. The difference from the structure of FIG. 5 resides in that the rolling diaphragm 8 turns its concave side to the working space 3. This involves that the pressure of the liquid must always be lower than the pressure in the working space 3. Consequently a force directed towards the working space must be exerted on the piston 2. This is achieved by providing the spring 50 in the form of a draw spring, while the shaft 41, rigidly secured to the piston 5 is now arranged above the weight 33 and the shaft 43, fixed to the piston 2 is arranged beneath the weight 33. The shaft 43 is adapted to move in an axial direction in slots provided on the prolonged portion of the piston 5. After the explanation given with reference to FIG. 5 the operation of the structure shown in FIG. 6 need not be described further. It should, however, be noted that the shaft and the slots may serve at the same time as stops for preventing the second piston from rising to an excessive height.

6 From the foregoing it will be apparent that the steps taken in accordance with the invention permit, in a particularly simple manner, of compensating the influences of t the inertia forces involved in devices comprising rolling diaphragm seals.

What is claimed is:

1. A device comprising at least one cylinder, a first piston adapted to reciprocate in said cylinder to thereby vary the volume of the work space therein, a rolling diaphragm seal betwen said first piston and the adjacent wall of said cylinder, at liquid column, means for maintaining on said rolling diaphragm seal and said first piston a pressure difference which is substantially constant at least during each stroke of said first piston, said first piston having its side remote from the work space in contact with said liquid column, a second piston, a driving gear, the side of said second piston remote from said driving gear being in contact with said liquid column, the side of said rolling diaphragm seal facing said second piston being in contact with said liquid column, means for compensating the inertia forces of said first piston plus the inertia forces of a quantity of liquid substantially corresponding to the volume of the space bounded by the side of said first piston engaging the liquid and the tangential plane of said rolling diaphragm seal substantially at right angles to the center line of said device and abutting said side of said rolling diaphragm seal when said first piston occupies a position approximately half way between the upper and lower dead positions of said first piston to an extent such that said forces do not substantially affect the pressure difference on the rolling diaphragm seal and said first piston, said means for compensating the inertia forces of said first piston plus the inertia forces of said quantity of liquid being at least one mass connected to said first and second pistons so as to be freely movable, said connection being such that the inertia force of said mass applies to the first piston in a direction opposite to the inertia forces of the first piston and said quantity of liquid.

2. A device as claimed in claim 1 further comprising a lever and means for pivoting said lever to said first and second pistons, said mass connected to and co-actin-g with said lever, the pivoting means for said second piston being located between said mass and the pivoting means for said first piston.

3. A device as claimed in claim 2 wherein said mass and the associated lever are located in the liquid between said first and second pistons.

4. A device as claimed in claim 1, wherein said means for maintaining a pressure difference on said rolling diaphragm seal are resilient members which engage said mass.

5. A device comprising at least one cylinder, a first piston adapted to reciprocate in said cylinder to thereby vary the volume of the work space therein, a rolling diaphragm seal between said first piston and the adjacent wall of said cylinder, a liquid column, means for maintaining on said rolling diaphragm seal and said first piston a pressure difference which is substantially constant at least during each stroke of said first piston, said first piston having its side remote from the work space in contact with said liquid column, a second piston, a driving gear, the side of said second piston remote from said driving gear being in contact with said liquid column, the side of said rolling diaphragm seal facing said second piston being in contact with said liquid column, at least one mass connected to said first and second pistons in a manner to be freely movable, su-ch connection being such that the inertia force of said mass applies to the first piston in a direction opposite to the inertia forces of the first piston and a quantity of said liquid column, said quantity of liquid substantially corresponding to the volume of the space bounded by the side of said first piston engaging the liquid and the tangential plane of said rolling diaphragm seal substantially at right angles to the center line of said device and abutting said side of said rolling diaphragm seal when said first piston occupies a position approximately half way between the upper and lower dead positions of said first piston, 21 cable-pulley system for linking said mass to said first and second positions so the inertia forces of said first piston plus the inertia forces of said quantity of the liquid column are neutralized by said mass.

6. A device as claimed in claim 5 wherein the transmission ratio of said cable-pulley system differs from unity.

7. A device as claimed in claim 5 wherein said cablepulley stem is located in the liquid between said first and second pistons.

8 References Cited UNITED STATES PATENTS Reitdijik 92-6O X OTHER REFERENCES Ham, C. W., et al.; Mechanics of Machinery, N.Y., McGraw-Hill Book Co., 1958, pages 349-660.

\MARTIN P. SCHWADRON, Primary Examiner. 1D I. C. COHEN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,372,624 March 12, 1968 Johan Adriaan Rietdijk It is certified that error appears in the above identified t and that said Letters Patent are hereby corrected as pat en shown below:

Column 4, line 51, for "level" read lever column 7, line 6, for "positions" read pistons line 14, for "stem" read system Signed and sealed this lst day of July 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

